JPH07173520A - Method for dephosphorizing chromium-containing molten iron and molten steel - Google Patents

Abstract

PURPOSE:To provide a method for dephosphorizing molten iron, by which the lowering of fluidity of flux caused by the oxidation of chromium is restrained and the uneconomical sorting of raw material is unnecessary and an expensive special device is not used and the sufficient effect in the plactical operation having good efficiency is obtd. at a low cost by using the inexpensive collected dust of an electric furnace as O2 source, in the dephosphorization for the molten iron and the molten steel containing >=1% chromium. CONSTITUTION:In the dephosphorizing method by charging the flux 3 for dephosphorizing into a ladle tapping the molten iron or the molten steel from a melting furnace or a refining furnace 1 or near the dropping position thereof to utilize the stirring force caused by the tapping stream, in order to prevent the lowering of the fluidity of flux caused by the oxidation of chromium, the phosphorizing is treated at the temp. (T) of the preceding oxidizing zone of carbon obtd. from Hilty's empirical equation log ([%Cr]/[%C])=-13800/T+8.76 or higher.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for dephosphorizing hot metal and molten steel (hereinafter referred to as molten iron) containing 1% or more of chromium in the operation of pig iron and steelmaking.

[0002]

2. Description of the Related Art Phosphorus in molten iron is an element that is generally harmful to the quality of steel, and its removal is an important issue in steelmaking technology. Generally, in the case of ordinary steel, the technology is almost established, but in molten iron containing chromium, phosphorus is desired due to the decrease of fluidity of slag due to formation of Cr ₂ O ₃ or the decrease of phosphorus activity due to chromium. It is extremely difficult in actual operation to economically reduce to the level. Therefore, the production of low-phosphorus molten iron is usually dealt with by using a raw material having a low phosphorus content.

An important factor affecting dephosphorization is the composition and addition method of the dephosphorization flux. For addition method,
The recently proposed addition method is, for example, Japanese Patent Publication No. 4-18.
No. 005, Japanese Patent Publication No. 2-7363 and Japanese Patent Laid-Open No. 1-20
No. 5024 each proposes a method of stirring and adding gas in an AOD furnace and a refining furnace having a stirring function such as AOD.

[0004]

DISCLOSURE OF THE INVENTION In the present invention, in dephosphorization of molten pig iron and molten steel containing 1% or more of chromium, deterioration of flux fluidity due to oxidation of chromium is suppressed, and uneconomical selection of raw materials is unnecessary. A highly efficient and inexpensive molten iron dephosphorization method that has a sufficient effect in actual operation by using inexpensive electric furnace dust collection dust as an O ₂ source without using any expensive special equipment. Regarding providing.

[0005]

A feature of the present invention resides in a method of adding a flux for dephosphorization. That is, the method is characterized in that the molten metal is charged into the ladle to be tapped from the melting furnace or the refining furnace or to the tapping flow or the vicinity of the dropping position, and the stirring force by the tapping flow is used.

For dephosphorization of molten iron, P is converted into P ₂ by the following chemical reaction.
It is performed by changing to O ₅ and capturing with CaO in the flux.

4 [P] + 5O ₂ → 2 (P ₂ O ₅ ) Here, solid oxygen such as scale or gaseous oxygen is used as the O ₂ source, and CaO--CaF ₂ system, Ca is used as the flux.
O-CaF ₂ -CaCO ₃ system, or CaO-CaF ₂ -
Although various known fluxes such as CaCl ₂ type can be used, the present invention particularly replaces the electric furnace dust collection dust as the O ₂ source with a part or all of the solid oxygen used.

As is well known, the dust collected in the electric furnace is Pd, C.
Since it contains harmful elements such as d, it is normally disposed of in landfill after stabilization treatment. However, by using the method of the present invention, a part of other valuable metals of Fe is recovered, and effective use of industrial waste is possible. Can be measured.

By the method of adding to the molten iron according to the present invention, these fluxes are rapidly dissolved, turned into slag and maintain fluidity, and are sufficiently mixed with molten iron to carry out the slag / metal interface reaction.

The stirring force in the addition method of the present invention is 10
It is 0 to 300 watt / t, which is 1/10 or less as compared with a refining furnace such as AOD. However, since the flux and the molten iron having greatly different specific gravities are sufficiently mixed, the object can be achieved.

On the other hand, the fluidity of the slag-like flux is significantly hindered by Cr ₂ O ₃ produced by the following reaction formula.

4Cr + 3O ₂ → 2Cr ₂ O ₃ This is the difficulty of dephosphorization in molten iron containing chromium, and it is possible to suppress the Cr ₂ O ₃ concentration in the slag to 10% or less, preferably 5% or less. is necessary. Cr above
_In order to suppress the ₂ O ₃ concentration, the selection of the dephosphorization treatment temperature is important, and it can be achieved by treating at a temperature higher than the temperature (T) calculated from the following Hilty's empirical formula.

Log ([% Cr] / [% C]) =-13
800 / T + 8.76 For example, when C = 4% and Cr = 5%, the processing temperature may be set to the limit temperature (T) = 1593 ° K (1320 ° C) or higher.

The above temperature conditions achieve a Cr ₂ O ₃ concentration in the slag of less than about 5% and a high dephosphorization rate, as will be illustrated in the examples.

[0015]

[Effect] As described above, the present invention provides an inexpensive and efficient method for dephosphorizing molten iron containing chromium, which contributes to improving the quality of molten iron containing chromium.

Further, by using the dust collected by the electric furnace, not only the cost of the flux becomes low, but also the F
e A part of other valuable metals is recovered, which contributes to reducing the amount of industrial waste.

[0017]

EXAMPLES Example 1 The arrangement of the test equipment is shown in FIG. About 2 tons of molten iron containing chromium was melted in the low-frequency induction furnace 1 into the atmosphere, and after adjusting the temperature, the flux for dephosphorization and the scale as the O ₂ source were placed and placed in the ladle 2 to be tapped. The dephosphorization test was carried out by two methods, in which the addition was made in the vicinity of the molten metal flow.

Table 1 shows the molten iron component before dephosphorization, the flux basic unit, the flux addition method and the treatment temperature at that time.

[0019]

[Table 1] All treatments were carried out at a temperature higher than the temperature (T) calculated from Hilty's empirical formula. The obtained dephosphorization rate is shown in FIG. 2 in relation to the scale unit. In each case, a high dephosphorization rate was obtained. The Cr ₂ O ₃ concentration in the slag was low as shown in FIG. 3, and the fluidity of the slag was good.

Example 2 Experiment No. 1 in Example 1 Under the same conditions as in No. 5, about half of the scale, 50 kg / t, was replaced with ordinary steel electric furnace dust collection dust. At that time, the dephosphorization rate was a high level of about 85%.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an arrangement of equipment for dephosphorization treatment.

FIG. 2 is a diagram showing the relationship between the scale unit and the dephosphorization rate.

FIG. 3 shows Cr ₂ O ₃ in slag in each test example.
It is the figure which showed the density.

[Explanation of symbols]

 1 Low-frequency induction furnace 2 Ladle 3 Flux for dephosphorization 4 Flux that has been placed 5 Flux that has been added to the hot water flow 6 Flux hopper

Claims (2)

[Claims] 1. A dephosphorization method for dephosphorizing hot metal and molten steel containing 1% or more of chromium, in which a flux for dephosphorization is introduced into a ladle to be tapped, or near the pouring stream or its dropping position. Hilty's empirical formula: log ([% Cr] / [% C]) =-13800 / T +
8.76, wherein the treatment is performed at a temperature equal to or higher than the temperature (T) in the preferential oxidation region of carbon determined from 8.76. 2. The method according to claim 1, wherein a flux mixed with dust collected in an electric furnace is used as an oxygen source for the dephosphorization reaction.